Traditionally, in order to protect a circuit from a surge, a protection circuit is included between the supply terminal and the ground terminal. This protection circuit operates only in the case a surge is applied to the supply terminal or the ground terminal. In general, a diode connected in the reverse direction between the supply terminal and the ground terminal is used in the protection circuit.
In the protection circuit, the diode permits an electric current to flow from the supply terminal to the ground terminal by breaking down when a surge current is applied thereto. However, when the breakdown voltage is high, the voltage at which the protection circuit begins to operate increases, and so the breakdown voltage of the protected circuit needs to be increased, which typically causes an increase in the size of the entire circuit.